1. Field of the Invention
This invention relates in general to a system for tensioning a section of casing extending between a subsea housing and a surface wellhead located on an offshore platform, and in particular to a system utilizing an adjustable mandrel.
2. Description of the Prior Art
In one type of offshore drilling, particularly with jack-up drilling rigs, a wellhead housing will be located at the platform. The string of casing in the well will be supported by a mudline hanger located in a subsea housing at the sea floor. The sections of casing above the subsea housing need to be tensioned.
U.S. Pat. Nos. 4,909,546 and 5,002,131 show systems for applying tension to the casing above a subsea housing. There have been other systems proposed also that employ a means to pull tension on the casing, a ratcheting means to ratchet during the upward movement of the casing, the ratcheting means then supporting the casing in tension when the upward pull is relaxed. While these systems are workable, improvements are desirable in reducing cost, and in providing greater ease in installation.